Exercise can have both positive and negative effects on immune function (and susceptibility to minor Illnesses).
Many studies have reported that part of the immune cell functions are temporarily impaired during prolonged heavy exercise, and those athletes appear to be more susceptible to minor infections.
During intense prolonged exercise there are increased levels of stress hormones that cause reducing in leukocytes capacities.
During exercise exposure to airborne pathogens is increased due to depth of breathing.
Chronic Effects Of Exercise Training On Immune Function:
During cross-section studies it has been found that levels of leukocytes in athletes, after more that 24 hours resting are almost the same as sedentary individuals.
Thus in the resting state, immune function appears to be almost similar in athletes and non-athletes.
New studies showed that the Immunoglobulin levels in athletes are higher than in non-athletes, else if the athletes are in periods of very heavy training.
While athletes at a periods of very heavy training, they have a dysfunction in the immune system, but it does not put them in danger of serious illness, but it increase their risk of picking up common infections such as URTI, or Influenza.
Several Longitudinal Studies:
Several Longitudinal Studies have monitored immune function in high-level athletes such as cyclists, swimmers and footballers, during a competitive season.
In a recent study of American football players, the incidence of UTRI was increased during intense training.
Another study monitored a cohort of elite Australian swimmers over a 7 – month training season in preparation for the national championships.
The results indicated significant depression of resting serum and salivary immunoglobulin concentrations in athletes, associated with long-term training at an intensive level.
A Small Price To Pay For Long-Term Health Benefits?
Extreme exercise stress may impair immune function and increase the chances to get infection, but this may not be entirely bad for the athlete and by reducing immune activation and subsequent inflammation, be one of the mechanisms through which regular exercise benefits long-term health.
Period of chronic exercise training can cause a post-exercise immunodepression and higher susceptibility to get infection, this may be a small price to pay as, over long term, a decrease in TLR expression may represent a beneficial effect, because it decreases the inflammatory capacity of leukocytes, thus altering whole body chronic inflammation and possibly reducing the risk of developing chronic disease.
In summary, heavy exercise cause a temporary depression of immune function, that lasts 3-25 hours after exercise, depending on the intensity of the exercise.
Periods of intensified training, last one week or more can result immune dysfunction for longer time.
Individuals do not need to perform heavy training in order to achieve the health benefits of exercise.